In U.S. Pat. No. 4,290,266 it is disclosed that a pipe loop can be placed in a blind bore in the earth and that a fluid can be passed down into the earth via a first section of the pipe loop and up from the earth via a second section of the pipe loop. A disadvantage of this prior art technique is that the said pipe loop sections extend very close to each other whereby upwardly flowing warm fluid is cooled by the cold, downwardly flowing fluid, with the result that the total efficiency is low.
Furthermore it is known that there are a number of deep bore holes or wells which have been used or are being used for the recovery of oil or gas together with associated installations above ground. As a consequence of the strain on the environment which these installations often represent, for environmental and other reasons increasing demands have been made for such installations to be removed or dismantled and the wells sealed after the oil or gas extraction has ceased, which is a very expensive process.